Nuclear facility flooding method

Abstract

To provide a method of flooding at least a portion of a nuclear facility experiencing a severe accident to shield radiation with water and enable underwater work.SOLUTION: A nuclear facility flooding method disclosed herein involves, in the presence of water leakage points in a water flow path to a water storage compartment associated with a nuclear facility having nuclear fuel debris generated by a severe accident, using at least one specific material in a region from the water storage compartment to the water leakage points to build a water blocking structure for stopping leakage from the water leakage points, and introducing water to the water storage compartment to flood at least a portion of the nuclear facility with water.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a decommissioning technique for a nuclear reactor that has suffered a severe accident. [Background technology]

[0002] In the event of a severe accident, including a core meltdown, at a boiling water nuclear power plant, the reactor containment vessel and reactor pressure vessel are damaged, making dismantling work extremely difficult in a flooded state. Furthermore, the high radiation levels inside the reactor building and the low water level make it difficult to identify damaged areas and repair water leaks. In such cases, fuel debris must be removed and the reactor building dismantled in an air environment. However, much of the dismantling work must be performed remotely, and measures must be taken to prevent the leakage of radioactive dust produced during cutting work during dismantling. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6960170 [Patent Document 2] Patent No. 5757222 [Patent Document 3] Patent No. 6186980 [Patent Document 4] Patent No. 7070998 [Patent Document 5] Patent No. 7071003 [Patent Document 6] Utility Model Registration No. 3196318 Summary of the Invention [Problem to be solved by the invention]

[0004] Various technologies have been known in the past. For example, the fuel debris treatment method described in Patent Document 1 aims to precipitate ultra-high specific gravity muddy water containing barite, solidify the fuel debris, and store it. However, no consideration is given to a method of flooding areas where nuclear fuel material or radioactive material remains.

[0005] Furthermore, the flooding methods for a containment vessel in Patent Documents 2 and 3 assume that there is a damaged area in the containment vessel, but that it is difficult to identify the damaged area, and so all of the space is filled with concrete. Because a large amount of radioactive waste will be generated, a watertight structure is constructed upstream of the anticipated damaged area, and the containment vessel is then flooded. This flooding method has the problem that a large amount of work must be performed inside the reactor building, which is subject to high radiation levels. Furthermore, no consideration is given to alternative or concurrent flooding methods in the event that workers' radiation exposure becomes high and work becomes difficult.

[0006] Furthermore, the reactor building flooding devices in Patent Documents 4 and 5 have a bottom constructed underground below the reactor building, and physically isolate the entire reactor building while flooding it. This is a very good concept as it reduces the risk of contaminated water leaking into the environment, but there are issues with this, such as the increased amount of work required, and in particular the need to construct an underground shield tunnel.

[0007] Furthermore, the nuclear reactor decommissioning support facility in Patent Document 6 constructs a pool that covers all of the multiple reactor buildings, and submerges the entire reactor buildings. However, there are issues such as the difficulty of constructing the bottom of the pool, the large scale of the pool, and the extremely large amount of water that the pool can hold.

[0008] An embodiment of the present invention has been made in consideration of these circumstances, and aims to submerge at least a portion of a nuclear facility that has suffered a severe accident, shield it from radiation with water, and enable work to be carried out in an underwater environment. [Means for solving the problem]

[0009] A method for flooding a nuclear facility according to an embodiment of the present invention involves constructing a water-stopping structure that stops water from leaking from a water flow path leading to a water storage compartment, which is a compartment related to a nuclear facility where fuel debris has been generated due to a severe accident, using at least one specific material between the water storage compartment and the leaking point, to prevent water from leaking from the water storage compartment, and introducing water into the water storage compartment to flood at least a portion of the nuclear facility. [Effects of the Invention]

[0010] According to an embodiment of the present invention, at least a portion of a nuclear facility that has suffered a severe accident can be submerged, providing radiation shielding with water and enabling work to be performed in an underwater environment. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram showing a water storage container, piping, and a leak location in the first embodiment. [Figure 2] Schematic diagram showing the process of constructing a water-stopping structure in a water storage container. [Figure 3] Schematic diagram showing the process of constructing a watertight structure in a pipe. [Figure 4] Schematic diagram showing the state where the leaking area has been sealed off. [Figure 5] 10 is a flowchart showing a water storage countermeasure method. [Figure 6] 10 is a flowchart showing a water storage countermeasure method. [Figure 7] 10 is a flowchart showing a water storage countermeasure method. [Figure 8] 10 is a flowchart showing a method for preventing water leakage outside the reactor building. [Figure 9] 10 is a flowchart showing a water stopping method. [Figure 10] FIG. 10 is a schematic diagram showing a water storage container, piping, and a leak location in a second embodiment. [Figure 11] Schematic diagram showing the process of constructing a water-stopping structure in a water storage container. [Figure 12] Schematic diagram showing the state where the leaking area has been sealed off. [Figure 13]FIG. 10 is a schematic diagram showing a pinch device, a water storage container, piping, and a leak location according to a third embodiment. [Figure 14] Schematic diagram showing the state in which a pipe is crushed by a pinch device. [Figure 15] Schematic diagram showing the process of constructing a water-stopping structure in a water storage container. [Figure 16] Schematic diagram showing the state where the leaking area has been sealed off. [Figure 17] FIG. 10 is a schematic diagram showing a strainer, a water storage container, piping, and a leakage location according to a fourth embodiment. [Figure 18] Schematic diagram showing the state where the leaking area has been sealed off. [Figure 19] FIG. 11 is a schematic view showing a state in which the pipe of the fifth embodiment is cut. [Figure 20] FIG. 10 is a schematic diagram showing the state in which the pipe is plugged. [Figure 21] FIG. 13 is a schematic diagram showing a state in which a balloon is injected into the piping of the sixth embodiment. [Figure 22] FIG. 13 is a schematic diagram showing a state in which an aggregation promoter is injected into a pipe according to the seventh embodiment. [Figure 23] Schematic diagram showing the state where the leaking area has been sealed off. [Figure 24] FIG. 13 is a schematic diagram showing a state in which water glass is poured into the piping of the eighth embodiment. [Figure 25] Schematic diagram showing the state of water glass solidified with carbon dioxide. [Figure 26] Schematic diagram showing the state where the leaking area has been sealed off. [Figure 27] FIG. 13 is a schematic diagram showing the state in which a weir material is introduced into the piping of the ninth embodiment. [Figure 28] Schematic diagram showing the state where the leaking area has been sealed off. [Figure 29] Schematic diagram showing the state in which a drone is inserted into a pipe in the tenth embodiment. [Figure 30] Schematic diagram showing the state where the leaking area has been sealed off. [Figure 31] FIG. 11 is a schematic diagram showing a state in which a blocking material is introduced inside and outside a pipe according to the eleventh embodiment. [Figure 32] Schematic diagram showing the state where the leaking area has been sealed off. [Figure 33]FIG. 23 is a schematic diagram showing a state in which a leak point in the twelfth embodiment is plugged. [Figure 34] FIG. 23 is a schematic diagram showing a process of injecting clean water into the piping of the thirteenth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the nuclear facility flooding method will be described in detail with reference to the drawings. Note that the shapes of the components shown in the drawings are simplified to facilitate understanding.

[0013] The nuclear facility flooding method is a method used to decommission nuclear power plants that have suffered severe accidents. Nuclear power plants contain a reactor building. Within this reactor building, it is necessary to remove fuel debris that has fallen to the bottom of the reactor containment vessel.

[0014] In the event of a severe accident, the fuel assemblies in a nuclear reactor melt due to overheating of the nuclear fuel, resulting in a so-called meltdown. The molten nuclear fuel leaks from the reactor pressure vessel contained inside the reactor containment vessel. The reactor containment vessel is also damaged by the increased pressure inside. Because fuel debris containing molten nuclear fuel is highly radioactive, even remotely operated robots may malfunction due to the effects of radiation if the work of removing the fuel debris is carried out using the partial submersion method. There is also a risk of workers being exposed to radiation.

[0015] If the fuel debris to be removed can be surrounded by water, the water can shield it from radiation. Furthermore, inside the reactor building, there are many areas with high radiation levels other than the fuel debris, and these also need to be submerged when being removed. Therefore, workers involved in the decommissioning work submerge at least a portion of the reactor building and the primary containment vessel. In the following explanation, the term "worker" includes multiple workers.

[0016] Furthermore, "nuclear facilities" includes various facilities installed in a nuclear power plant, such as the reactor building, reactor well, reactor containment vessel, reactor pressure vessel, pressure suppression chamber, pedestal, vent pipe, control rod drive mechanism, and reactor core.

[0017] Reference numeral 1 in Fig. 1 denotes a specific water storage vessel 1 that constitutes part of a nuclear facility. This water storage vessel 1 is a section related to the nuclear facility where fuel debris has been generated due to a severe accident, such as a reactor containment vessel. The water storage vessel 1 is the water storage section that is the target for storing water.

[0018] A specific pipe 2 is connected to the water storage container 1 as a distribution path (distribution flow path). The pipe 2 extends from the water storage container 1 to another location. A damaged portion 3 (leakage point) is present in a portion of the pipe 2, and a water leak 4 is occurring at this damaged portion 3. In other words, a water leakage point exists in the water distribution path leading to a water storage compartment where water can be stored. The damaged portion 3 may have been caused by a severe accident, or may have been caused by subsequent deterioration of the pipe 2.

[0019] Even if water is poured into this water storage container 1, the water leaks from the broken point 3 in the pipe 2, and the water level does not rise above the position where the pipe 2 is connected, that is, the position of the opening 5 of the pipe 2. In the example of Figure 1, inside the water storage container 1, the area below the opening 5 is a water region 7 as a water storage area, and the area above the opening 5 is a gas phase region 6. In order to fill the area above the opening 5 inside this water storage container 1 with water and flood the entire inside of the water storage container 1, it is necessary to stop the water leaking from the pipe 2.

[0020] The nuclear facility flooding method involves constructing a watertight structure that uses at least one specific material to stop water leakage from a leaking location, and then injecting water into a water storage compartment to flood at least a portion of the nuclear facility.

[0021] A water stopping method according to a first embodiment will be described with reference to Figures 1 to 4. For example, the water stopping method will be described in which a microparticle dispersion is injected into the interior of a water storage container 1, which is a water storage compartment.

[0022] The specific object of the first embodiment includes a microparticle dispersion. This microparticle dispersion includes water and microparticles having a specific gravity greater than that of water. Workers use this microparticle dispersion to construct a watertight structure that stops water from leaking from a location.

[0023] For example, a microparticle dispersion is injected into the water storage container 1, which is the internal space of the nuclear facility related to the leak location, and the microparticles are deposited to a height higher than the leak location, forming a microparticle sediment layer 8 (Fig. 2). When the microparticle dispersion is injected into the water storage container 1, the microparticles, which have a higher specific gravity than water, gradually settle and accumulate downward, forming the microparticle sediment layer 8. This microparticle sediment layer 8 is a water-stopping structure.

[0024] Furthermore, the microparticle dispersion liquid is also injected into the pipe 2, forming a microparticle deposition layer 8 (Fig. 3). In this way, it is possible to waterproof the damaged portion 3 of the pipe 2. Furthermore, water is injected up to a predetermined height. Then, the fuel debris is removed with at least the entire interior of the water storage container 1 submerged in water (Fig. 4).

[0025] The microparticles contain at least barite as a weighting material, and optionally at least bentonite as a thickener. The microparticles are deposited without solidifying, and are a water-stopping material with fluidity. The blending ratio of materials such as barite and bentonite is adjusted in advance so that the microparticles have such properties. The deposited microparticles can be made to flow again by applying vibration. In other words, even in a location where a microparticle deposition layer 8 has already formed, the microparticle deposition layer 8 can be washed away by applying vibration. Note that modes of applying vibration include modes of stirring.

[0026] The fine particle deposition layer 8 has fluidity, and various devices can access the fuel debris even when the fuel debris is buried in the fine particle deposition layer 8. In other words, in the following explanation, the state in which the fuel debris is buried in the fine particle deposition layer 8 and the state in which the fuel debris is submerged in water are almost the same state and have the same meaning.

[0027] The fine particles may also be a combination of fine particles with different particle sizes, including two or more of barite, bentonite, polymer, nuclide adsorbent (adsorbent that adsorbs radioactive materials), and boric acid. These fine particles maintain fluidity after deposition. The deposited fine particles can be re-fluidized by applying vibration.

[0028] The specific object includes an obstacle that hinders the flow of water, such as at least one of jigs, interference materials, heavy muddy water, concrete, grout, mortar, resin, filler, buffer material, zeolite adsorbent, titanate adsorbent, titanium silicate material, neutron absorbing material, cuttings, chips, slag, dross, spatter, abrasives, sand, and a mobile robot.

[0029] The nuclear facility flooding method is carried out by workers performing each step of the flowcharts in Figures 5 to 9. The nuclear facility flooding method is carried out to submerge the fuel debris in water, that is, to at least flood the fuel debris. These flowcharts show strategies for storing water in water storage compartments, which are areas where water can be stored, inside the nuclear facility to be flooded, until the target water level is reached.

[0030] In the following explanation, "water storage" includes a state in which no water is leaking from the water storage compartment. Also, a state in which a predetermined water level is maintained in the water storage compartment and water leaking from the water storage compartment does not mix with the groundwater around the nuclear facility is also included in the state in which "water storage" exists. Even if there is a small amount of water leakage, "water storage" exists as long as the predetermined water level is maintained in the water storage compartment.

[0031] First, the nuclear facility flooding method will be described using the flowcharts of Figures 5 to 9. The flowcharts include actions and effects that are passively produced by carrying out this nuclear facility flooding method. The following description covers at least some of the steps included in the nuclear facility flooding method, and other steps may also be included in the nuclear facility flooding method.

[0032] The water storage countermeasure method shown in Figures 5 to 7 is a flowchart for securing a water storage compartment for underwater fuel debris removal and dismantling of nuclear facilities. The water leakage countermeasure method to the outside of the reactor building shown in Figure 8 is a flowchart for suppressing water leakage to the outside of the reactor building.

[0033] First, in step S1 of FIG. 5, an operator sets a target water storage section and a target water level.

[0034] In the next step S2, workers inject water from the upstream side of the water storage container 1 (FIG. 1) serving as the water storage compartment. This water injection includes, for example, reactor water injection for cooling the reactor and water injection for storing water up to a predetermined water level in the water storage compartment.

[0035] In the next step S3, the worker determines whether the water level in the water storage compartment has risen. This determination includes determining whether the amount of water and radioactive material leakage is below the allowable value. Here, if the water level in the water storage compartment has risen and the amount of leakage is below the allowable value (YES in step S3), the process proceeds to step S4. On the other hand, if the water level in the water storage compartment has not risen and the amount of leakage exceeds the allowable value (NO in step S3), the process proceeds to step S5.

[0036] In step S4, which is reached if the answer to step S3 is YES, the worker determines that water stoppage measures are not necessary and completes the water storage measure method.

[0037] For example, there are cases where the water level in the water storage compartment has risen to the target level and leakage from the target water storage compartment 4 is managed without further leakage outside the reactor building. Or there are cases where radioactive materials are below the detection limit, which is the allowable value. In these cases, if the situation is satisfactory from the perspective of radiation protection for the inside and outside environments of the reactor building, workers will determine that water stoppage measures are not necessary or that water stoppage measures have been completed.

[0038] In step S5, which is reached if step S3 is NO, the operator determines whether it is possible to identify the leak location from the appearance of the nuclear facility. This determination includes determining whether it is possible to detect the amount of leakage. Here, if it is possible to identify the leak location from the appearance (if YES in step S5), the process proceeds to step S6. On the other hand, if it is not possible to identify the leak location from the appearance (if NO in step S5), the process proceeds to step S24 (Figure 7).

[0039] For example, there may be cases where the location of the leak is unknown. There may also be cases where it is not possible to determine whether the amount of leakage is commensurate with the amount of water injected, meaning that it cannot be said with certainty that all leakage has been detected. There may also be cases where a leak has been identified, and although the location of the leak can be grasped to a certain extent, the leak path or opening location cannot be identified, making it difficult to consider a specific water-stopping method. In such cases, since the leak situation cannot be fully determined, the process proceeds to step S24 (FIG. 7) in which, together with the newly discovered information, a water-stopping method for the unconfirmed leak location within the range of the water storage compartment and the water distribution path (distribution flow path) is selected.

[0040] On the other hand, if the worker identifies the location and amount of leakage and there is a possibility of selecting a specific water-stopping method for this leakage location, the process proceeds to step S6, where it is determined whether it is necessary to apply the water-stopping method to the identified leakage location.

[0041] In step S24 of FIG. 7, which is reached if the answer is NO in step S5 (FIG. 5), the worker selects a water stoppage measure for the unconfirmed leak location within the water storage compartment and the water distribution path (distribution flow path).

[0042] In the next step S25, the worker considers the specific waterproofing material, material, particle size, specific gravity, injection amount, and transfer method.

[0043] For example, if there are multiple water storage compartments, workers cannot simultaneously visually check the components of all of the water storage compartments. Therefore, workers may need to select a water stop method for an unconfirmed leak location within the water storage compartments and water distribution route (distribution flow path). In this case, workers will consider the specific water stop material, material, particle size, specific gravity, injection amount, and transfer method, taking into account the design information and damage status of the nuclear reactor or other nuclear equipment, even if the specific leak location is not yet known.

[0044] In the next step S26, the worker reviews the construction work based on the results of reviewing the specific waterproofing material, material, particle size, specific gravity, injection amount, and transportation method, and then proceeds to step S12 (FIG. 6).

[0045] In planning the work, workers will generally plan to approach from the upstream side of the water storage compartment. However, there are cases where water stoppage work is carried out in conjunction with or in conjunction with local water stoppage methods. Therefore, there are cases where approach is planned within the range from the leak point to the upstream side of the water storage compartment. In particular, it is necessary to minimize work inside the reactor building to reduce exposure and reduce the amount of contaminated construction equipment. Therefore, this overall work and the local work described below will mutually consider applying common equipment in as similar a layout as possible. Based on the results of this work plan, procedure, and impact review, workers will move on to a comparative evaluation of the water storage effects of the construction method (Step S12).

[0046] In step S6 (FIG. 5), which is reached if step S5 is YES, the worker determines whether or not it is necessary to take water-stopping measures at the identified leak location. If it is necessary to take water-stopping measures at the identified leak location (if YES in step S6), the worker proceeds to step S7 (FIG. 6). On the other hand, if it is not necessary to take water-stopping measures at the identified leak location (if NO in step S6), the worker proceeds to step S24 (FIG. 7).

[0047] For example, there may be cases where the amount of leakage is small, or the water clearly does not contain radioactive materials, and it is determined that the source of the leaked water is clearly not from the water storage compartment, such as rainwater inflow. In this case, in order to reduce the amount of contaminated water, a water stoppage method for the unconfirmed leak point within the water storage compartment and the water distribution route (distribution flow path) is selected.

[0048] On the other hand, if a leak is evident and would have a significant impact on the effectiveness of water-stopping work at the identified leak point, it is necessary to reduce the amount of leakage as soon as possible. Also, when the water level in the water storage section rises to the target level, the amount of leakage may exceed the capacity of the water leakage treatment device (not shown) due to the relationship with the hydraulic head pressure. Therefore, it is necessary to reduce the amount of leakage even if only slightly. In such cases, water-stopping measures for the identified leak point are selected.

[0049] 6, which is performed if the answer to step S6 is YES, the worker selects a water-stopping measure for the identified leak location. For example, the worker identifies the minimum required water storage compartment and the area where water leakage countermeasures are required.

[0050] In the next step S8, the worker examines the water distribution path (distribution flow path). For example, the worker examines to identify the upstream part of the leak location. Here, the distribution path extending from the water storage compartment and its upstream side may include the vent pipe of the reactor containment vessel, the closure plate of the penetration part of the reactor containment vessel, the connecting equipment of the system piping penetrating to the outside of the reactor containment vessel, the nozzle opening of the reactor pressure vessel, etc.

[0051] In the next step S9, the worker determines whether or not the distribution route is accessible from the upstream side. If the distribution route is accessible from the upstream side (YES in step S9), the process proceeds to step S10. On the other hand, if the distribution route is not accessible from the upstream side (NO in step S9), the process proceeds to step S20 (FIG. 7).

[0052] For example, whether or not access to the distribution route from the upstream side is permitted is determined based on the results of a previous on-site investigation, such as the design information of the nuclear power facility and an investigation of the inside of the reactor containment vessel. Note that, in this determination, newly required on-site investigations may be identified and carried out.

[0053] In step S10, which is reached if step S9 is YES, the worker determines whether or not plugging the distribution route is possible. If plugging the distribution route is possible (YES in step S10), the process proceeds to step S11. On the other hand, if plugging the distribution route is not possible (NO in step S10), the process proceeds to step S17 (FIG. 7).

[0054] Plugging refers to, for example, placing a plugging plug 33 in the opening 5 of the nozzle or pipe 2, as shown in Figure 33. If plugging is difficult due to damage caused by a severe accident or an obstructing structure, proceed to step S17 (Figure 7).

[0055] In step S11 (FIG. 6), which is the step to proceed to if the answer is YES in step S10, the worker considers the construction plan, procedure, and impact of a water stoppage plan as one of the leak prevention measures. The construction plan basically includes planning an approach from the upstream side of the water storage section.

[0056] In the next step S12, the workers will compare and evaluate the effects and impacts of the water storage methods. Note that the workers will not proceed to the next step until the study of measures to prevent water leakage to the outside of the reactor building is completed and candidate methods for preventing water leakage from all water storage compartments have been identified.

[0057] However, even if it is determined that plugging the opening 5 (Fig. 33) of the piping 2, which is the distribution channel (distribution flow path), is possible, the target water-stopping performance may not be achieved due to the effects of damage caused by a severe accident. Furthermore, external factors such as earthquakes, interference during work, and internal factors such as radiation degradation of the sealing material used in the plugging plug 33 (Fig. 33) may cause leakage from the plugging plug 33. Furthermore, the amount of leakage may increase. To prepare for such future risks of not achieving performance, as well as for transient, abnormal, and emergency situations, it is advisable to adopt multiple leak prevention measures. In step S20 (Fig. 7), such alternative and combined plans may be considered.

[0058] In step S17 of Figure 7, which is performed if step S10 is NO, the operator determines whether the leaked water can be replaced with clean water. If the leaked water can be replaced with clean water (if YES in step S17), the operator proceeds to step S18. On the other hand, if the leaked water cannot be replaced with clean water (if NO in step S17), the operator proceeds to step S20. Note that a case in which the leaked water cannot be replaced with clean water may occur, for example, when the dilution effect cannot be obtained due to insufficient transfer or transfer amount of clean water.

[0059] In step S18, which is reached if the answer is YES in step S17, the worker examines the construction plan, procedure and impact of clean water injection as one possible measure to prevent leakage to the outside of the reactor building.

[0060] When replacing leaked water with clean water, the amount of leakage cannot be reduced, so it is necessary to consider the concentration and dilution rate of radioactive materials in the subsequent fuel debris removal work and equipment dismantling work. Furthermore, a water leakage treatment device (not shown) may be installed to prevent leaked water from mixing with the groundwater around the reactor building, but the amount of leakage must not exceed the capacity of this device. Therefore, it is necessary to reduce the amount of leakage as much as possible.

[0061] In the next step S19, the worker determines whether or not the injection of clean water will be effective based on the results of the review of the construction plan, procedure, and impact of the clean water injection. For example, the worker predicts the amount of water and radioactive material leaked. If the injection of clean water will be effective (YES in step S19), the process proceeds to step S12 (FIG. 6). On the other hand, if the injection of clean water will not be effective (NO in step S19), the process proceeds to step S20.

[0062] The construction plan for clean water injection basically involves planning an approach from the upstream side of the water storage compartment. If clean water injection is effective, the process proceeds to step S12 (Fig. 6), where a comparative evaluation of the water storage effects and impacts of the construction method is carried out. Note that in step S12, workers will not proceed to subsequent steps until the process of examining measures to prevent water leakage outside the reactor building is completed and candidate construction methods for water stoppage measures for all water storage compartments have been identified.

[0063] However, even if clean water replacement is possible in the distribution channel (distribution flow path), the target dilution performance may not be achieved, even temporarily, depending on the radioactive concentration of contaminated water in the water storage compartment during fuel debris removal work and cutting work in equipment dismantling work. External factors such as earthquakes may cause displacement of the clean water transfer pipe. Internal factors, such as temporary removal due to interference during work, may also reduce the clean water transfer capacity. To prepare for such future risks of not achieving performance, transient, abnormal, and emergency situations, it is possible to adopt multiple leak prevention measures. In step S20 (Figure 7), such alternative and combined plans may be considered. Furthermore, the approachable range from the leak location to the required water storage compartment may also be considered.

[0064] In step S20 (FIG. 7), which is carried out if step S9 is NO or if step S19 is NO, the worker considers the accessible range from the leak location to the required water storage compartment.

[0065] Here, we will explain how to consider the approachable range from the leak location to the required water storage compartment. For example, workers conduct and organize a predetermined investigation according to the target section along the distribution route (distribution flow path) considered in step S8 above. This investigation and organization includes design information and on-site investigation, such as the cross-sectional shape, dimensions, and cross-sectional area of ​​the distribution route, the floor and location inside the reactor building where the work will be performed, obstacles to the target section, the layout and dimensions of the area where workers will move, and atmospheric dose distribution.

[0066] In the next step S21, the worker selects an applicable local water-stopping method based on the results of the investigation and organization.

[0067] The localized water-stopping method uses various injection devices (not shown). These injection devices can be shared. For example, they can be shared by changing the mixture of materials to be injected. They can also be shared by shifting the position of the target area.

[0068] In the next step S22, the worker considers possible combinations of the selected local water stoppage methods.

[0069] In the next step S23, the worker considers the local water leakage prevention work plan, procedure, and impact. This local water leakage prevention work plan basically includes planning the approach range from the leak location to the upstream side of the water storage section. Then, proceed to the above-mentioned step S12 (FIG. 6).

[0070] Based on the results of the study of the local water stoppage work plan, procedure, and impact, workers will conduct a comparative assessment of the water storage effects and impacts of the work methods in step S12. Note that the work will not proceed to the next step until the study of measures to prevent water leakage to the outside of the reactor building is completed and candidate methods for preventing water leakage from all water storage compartments have been identified.

[0071] The following information is reflected in the process of identifying candidate construction methods for a water storage strategy for a specific leak location. For example, the results of a determination on whether or not it is possible to approach the distribution route (distribution flow path) from upstream reflect information that access is not possible. Also, the construction plan reflects the plugging construction plan, procedures, and impact study results. Also, the results of a determination on whether or not it is possible to replace the leaked water with clean water reflect information that replacement is not possible. Also, the clean water injection construction plan, procedures, and impact study results, and the local water stoppage construction plan, procedures, and impact study results are reflected. Also, specific water stoppage methods for unconfirmed leak locations within the water storage section and water distribution route are considered.

[0072] In step S12, the worker does not proceed to the next step until the study of measures to prevent water leakage to the outside of the reactor building is completed.

[0073] Next, a method for preventing water leakage outside the reactor building shown in FIG. 8 will be explained.

[0074] When considering leak prevention measures for the reactor building, workers understand the groundwater trends around the reactor building and set conservative target water levels inside the reactor building so that the water level inside the building is always lower than the groundwater level.

[0075] First, in step S31, workers measure the groundwater level around the reactor building. This measurement can be achieved, for example, by digging a pit for observing the groundwater level. The groundwater level is expected to fluctuate due to seasonal factors such as weather. This measurement of the groundwater level around the reactor building is performed to set a conservative minimum groundwater level. Note that this minimum groundwater level may be revised as appropriate depending on future measurement results.

[0076] In the next step S32, the worker determines whether the groundwater level is equal to or higher than the water level at the time of the large-scale water leak. If the groundwater level is equal to or higher than the water level at the time of the large-scale water leak (YES in step S32), the process proceeds to step S34. On the other hand, if the groundwater level is lower than the water level at the time of the large-scale water leak (NO in step S32), the process proceeds to step S33.

[0077] A large-scale water leak occurs when an external factor such as an earthquake causes the leak area to expand or a new break or penetration defect occurs in the water storage compartment, resulting in a large-scale water leak.

[0078] In step S33, which is reached if the answer is NO in step S32, the worker examines the clean water storage facility to be constructed around the reactor building, and then the process proceeds to step S34.

[0079] For example, a comparative assessment of the impact of the water storage compartment, the designated water level, the water storage effect of the construction method, and these are carried out. Here, various considerations are carried out based on the prerequisites of the leakage prevention method from the candidate water storage compartment, the water stoppage area, the normal water storage volume when the water is stopped, the distribution of radioactive materials, and the expected leakage volume.

[0080] As a result of the study, if a large-scale leak were to occur due to an external factor such as an earthquake, and the groundwater level were to rise, it would be necessary to surround the reactor building with a pit and construct a dam. Furthermore, construction work to store clean water would be necessary. For example, workers would excavate around the reactor building's frame to build a pit and construct a dam to store clean water, in order to maintain a minimum groundwater level.

[0081] In this way, the reactor building is surrounded by a dam that stores clean water to constantly replenish the groundwater level, so even if a water leak occurs that exceeds the groundwater level, the water will not leak outside the reactor building.

[0082] It is also possible that the leaked water will cause the reactor building to flood above the first floor. In this case, a separate water storage tank and water transfer device will be installed outside the reactor building. The transfer device could be a pump, for example.

[0083] If the answer is YES in step S32 or in step S34 which follows step S33, the worker determines whether or not seismic reinforcement of the containment vessel is feasible. If the answer is YES in step S34, the worker proceeds to step S35. On the other hand, if the answer is NO in step S34, the worker returns to step S1 (FIG. 1).

[0084] This determination is important in establishing preventive measures to prevent the occurrence of the aforementioned large-scale water leakage. Therefore, it is particularly necessary to prevent large-scale damage to important structures related to the reactor containment vessel, such as the pressure suppression chamber and vent pipes. For example, it is possible to fix and support the pressure suppression chamber by injecting grout into the basement floor of the reactor building. In this way, even if water leaks from the water storage compartment due to large-scale damage caused by external factors such as an earthquake, the water level in the basement floor can be maintained.

[0085] If the seismic reinforcement of the reactor containment vessel is not successful, the process returns to step S1 (Fig. 1) and the target setting is revised to be lower.

[0086] In step S35, which is reached if the answer to step S34 is YES, the operator sets the target water level for the basement floor of the reactor building.

[0087] In the next step S36, the worker measures the water level in the basement of the reactor building and sets up the drainage equipment, and then the process proceeds to step S12 (FIG. 6).

[0088] The series of studies to prevent water leakage outside the reactor building can be done through desk studies and design studies. It can also be carried out in stages, from when all water storage measures have been clarified until the start of water storage in the water storage compartment. It is sufficient to carry out the work in time according to the target water level setting.

[0089] It is also possible to maintain a state in which groundwater not containing radioactive materials flows into the reactor building according to the difference in hydraulic head pressure between the inside and outside of the reactor building. In this way, it is possible to prevent water from leaking outside the reactor building and prevent the spread of radioactive materials. It is also possible to interpret the water level in the basement as the water level inside the reactor building. It is also possible that the maximum water depth in the basement inside the reactor building may exceed the groundwater level.

[0090] The watertight method and its watertight structure can be installed throughout the entire reactor building. Furthermore, in the future, the time required for water permeation, the purification performance of radioactive materials during water permeation, and the decontamination factor may become clear. Furthermore, the range of radioactive material impregnation may become clear. Furthermore, the radioactive material may fall below the detection limit. In these cases, the above-mentioned settings may be changed as appropriate.

[0091] Once the method for preventing water leakage outside the reactor building has been decided, a comparative evaluation of the effectiveness and impact of water storage measures will be conducted again. As a result, specifications for target water level management and drainage facilities in the basement of the reactor building will be presented.

[0092] The comparative evaluation of the water storage effect and impact of the prescribed water stopping method mainly includes matters such as workability, worker exposure, environmental load, hazardous substances, amount of radioactivity released, construction period, amount of construction work, water stopping success rate, predicted water storage amount, predicted leakage amount, external factor soundness, and predicted equipment deterioration.

[0093] In step S13, which follows step S12 in FIG. 6, the worker determines whether the considered water-stopping method satisfies construction feasibility. This determination includes determining the results of an evaluation of the impact on the surrounding environment. If construction feasibility is satisfied (YES in step S13), the process proceeds to step S14. On the other hand, if construction feasibility is not satisfied (NO in step S13), the process returns to step S1 (FIG. 1). If the result of this determination is that the method is insufficient, the method will be reviewed from the beginning.

[0094] In step S14, which is reached if the answer to step S13 is YES, the worker determines the watertight construction method and the order in which to carry out the watertight construction, and then the process proceeds to steps S15 and S16.

[0095] In step S15, the worker performs the overall or local construction work, and then the process returns to step S2 (FIG. 1).

[0096] In step S16, workers carry out earthquake-resistance reinforcement, measure the water level in the basement, and install drainage facilities, completing the flow chart.

[0097] During overall or localized construction work, water is injected upstream of the water storage compartment as needed. During this process, new leaks may be discovered. In such cases, workers will review the leak prevention measures as appropriate, linking the water storage measures with the measures to prevent water leakage into the reactor building, with the current construction work as a prerequisite.

[0098] Furthermore, as water is stored, radioactive materials such as fuel debris can cause radiolysis of the water, generating hydrogen. This hydrogen can be diluted by injecting inert gases such as nitrogen into the gas phase inside the reactor containment vessel. Alternatively, the gas phase containing hydrogen can be evacuated and purified, and measures to prevent hydrogen explosions can be implemented.

[0099] Furthermore, there is a possibility that criticality may occur due to the migration and accumulation of fuel debris in the reservoir water. Therefore, workers may mix a criticality prevention agent into the specific materials to be poured in. In this way, criticality can be prevented.

[0100] Furthermore, the operator may mix radioactive adsorbents such as zeolite, titanate, and titanium silicate into the permeable material, thereby removing radioactive materials from the water that passes through the material.

[0101] Next, an embodiment of the nuclear facility flooding method will be specifically described. The above-mentioned drawings may be referred to as appropriate. An operator carries out the nuclear facility flooding method in accordance with the above-mentioned flowcharts (FIGS. 5 to 8).

[0102] For example, it is assumed that even if water is injected into the reactor containment vessel, the water level does not rise. As shown in Figure 10, the reactor containment vessel is a water storage vessel 1 serving as a water storage compartment. A specific pipe 2 extends from the reactor containment vessel. This pipe 2 is a water distribution path (distribution flow path). This pipe 2 passes through another isolation vessel 10 serving as an isolation compartment. This isolation vessel 10 is a compartment related to a nuclear facility where fuel debris was generated due to a severe accident, such as a pressure suppression chamber or a specific room in a reactor building. There is a damaged area 3 (leakage area) in part of this pipe 2, and water leakage 4 is occurring at this damaged area 3.

[0103] First, the worker sets the target water storage compartment and the target water level. For example, the worker sets the target water level to be below a specified penetration hole on the first floor of the reactor containment vessel.

[0104] Next, workers inject water from the upstream side of the water storage container 1. This water injection is, for example, reactor water injection to cool the inside of the reactor where fuel debris exists.

[0105] Next, the worker determines whether the water level in the water storage container 1 has risen and whether the amount of water and radioactive material leaking is below the allowable value. If the determination is not satisfied or achieved, the worker determines whether the leak location and amount can be detected from the appearance of the water storage container 1.

[0106] However, if the workers are unable to detect the specific leak location, they will select a water-stopping method for the unconfirmed leak location within the water storage compartment and water distribution route (distribution flow path).Taking into account the design information and damage status of nuclear equipment such as nuclear reactors, workers will consider and select a water-stopping method to suppress water leakage, even if the specific leak location is not known.In addition to this newly discovered information, the workers will select a water-stopping method for the unconfirmed leak location within the water storage compartment and water distribution route.

[0107] Next, the workers will conduct a detailed study to select a water-stopping method for any unconfirmed leaks within the water storage compartment and water distribution route.

[0108] In this case, it is difficult to identify the location of the leak, but the height of the leak can be predicted from the water level (height) of the stored water inside the reactor containment vessel and information such as the design drawings of the reactor.

[0109] In this case, it can be seen that a leakage volume equivalent to the amount of water injected into the reactor occurs from the liquid-contacting surfaces of the pressure suppression chamber and the containment vessel via the vent pipe. Therefore, the minimum necessary water storage compartment is the space surrounded by the inlet of the vent pipe and the inner surface of the containment vessel. Therefore, if the space surrounded by the outer surface of the pedestal and the containment vessel can be filled with a predetermined water-stopping structure, the target water level can be achieved. Note that a microparticle dispersion liquid may also be injected into these spaces to form a microparticle sediment layer 8 (Figure 12).

[0110] It is also necessary to reduce the outflow of fine particles from the vent pipe opening. To achieve this, workers inject auxiliary deposits, such as grout, which are fluid even when poured underwater and subsequently solidify underwater, and then layer these auxiliary deposits. This method restrains the fine particle deposit layer 8 (Figure 12) and provides a fixed surface on which new fine particle deposit layers 8 can be layered. By repeating this process and layering the fine particle deposit layer 8 and auxiliary deposit layers alternately, the vent pipe opening can be efficiently sealed off. Furthermore, as mentioned above, it is possible that fine particles will adhere to and accumulate at the leak point on the side of the reactor containment vessel before being buried in the auxiliary deposits, leading to blockage and a reduction in the amount of leakage.

[0111] In other words, the nuclear facility flooding method involves alternately injecting fine particles and auxiliary deposits into the internal space of the nuclear facility, forming a multi-layered fine particle deposition layer 8 (Figure 12) in which layers of fine particles and layers of auxiliary deposits are alternately deposited.

[0112] The worker sets up an injection device (not shown) for injecting the microparticle dispersion. Here, the injection device injects the microparticle dispersion until it reaches a predicted height position, forming a microparticle deposition layer 8. It is sufficient that the height position of the leakage point is at least predicted. The worker also sets up a drainage device (not shown). Here, the drainage device prevents water leakage from a leakage point located above the target water level, and can also properly drain and manage the supernatant of the microparticle dispersion.

[0113] In addition, in order to consider measures to prevent water leakage outside the reactor building, workers first grasp the trend of the groundwater level around the reactor building.

[0114] Next, workers determine whether the groundwater level will be higher than the water level in the reactor building when a large-scale leak occurs. Here, the main locations to be watertight are, for example, the entrance to the vent pipe and the side of the reactor containment vessel. The maximum radioactive material concentration is assumed to be the maximum concentration when the fuel debris is cut and processed. Alternatively, a homogeneous distribution of radioactive material concentration when the fuel debris is cut and processed is assumed. The amount of leakage is assumed to be the rupture of the vent pipe. The water volume at the height between the bottom of the vent pipe opening and the target water level is also input and becomes a prerequisite for the study.

[0115] Here, the target water level is the first floor of the reactor building. When workers determine whether the groundwater level will be equal to or higher than the water level in the reactor building when a large-scale leak occurs, they assume that the groundwater level will always be equal to or higher than the water level in the reactor building.

[0116] Next, workers will conduct a seismic assessment of the reactor containment vessel and an assessment of the feasibility of seismic reinforcement.

[0117] In order to prevent the vent pipe from breaking, it would be effective to reinforce the suppression chamber against earthquakes by pouring grout into the basement floor. Furthermore, if the water level in the basement floor is lower than the groundwater level in the event of large-scale damage to the water storage compartment due to external factors such as an earthquake, the earthquake-resistant construction plan currently under consideration would be viable.

[0118] After this evaluation, the target water level inside the reactor building is set. Workers measure the water level in the basement of the reactor building and set up the drainage system. At this point, the specifications for the water level measurement and drainage system in the basement will be established.

[0119] On the other hand, if the water level in the basement of the reactor building becomes too high, the construction plan will be deemed invalid. The workers will re-establish the water storage compartment and water level target. In their re-examination, the workers will not only lower the target water level for the reactor containment vessel, but also set a target water level for the suppression chamber. The workers will also aim to reduce the weight of the structures used in the construction work and reduce the height of the grout required for seismic reinforcement. The workers may also consider the possibility of taking measures to stop water from the suppression chamber, just as they did for the reactor containment vessel.

[0120] Next, the workers will conduct a comparative assessment of the water storage effectiveness and impact of the water stopping methods.

[0121] For example, if the results of the re-examination show that the water level in the aforementioned basement floor is high, they can be compared with the results of the previous examination. In particular, workers will review the situation until they are able to prevent water from leaking outside the reactor building. For example, the assumption of large-scale structural damage could be revised from a complete rupture of the vent pipe to a partial opening of the vent pipe. Furthermore, it could be considered to increase the drainage capacity from the basement floor and review its conditions.

[0122] If the impact assessment and construction feasibility study find that the predefined conditions are met, the workers decide on the construction methods to be applied and the order in which to apply them. Then, the workers consider overall or localized construction work. Then, the workers carry out earthquake-resistance reinforcement, measure water levels in the basement, and install drainage facilities.

[0123] In addition, in the case of a nuclear reactor containment vessel, a case is assumed in which the water level is maintained below the opening of the vent pipe. In such a case, workers place a water level gauge for the reactor containment vessel, a microparticle dispersion injection device (not shown), and a drainage device (not shown) in the reactor containment vessel. Then, the workers alternately inject a predetermined auxiliary deposit and the microparticle dispersion into the reactor containment vessel. After the vent pipe is buried, the workers check whether there is any water leakage from the inner surface of the reactor containment vessel above the vent pipe and from the opening of the reactor pressure vessel. In particular, workers can narrow down the target by identifying in advance the systems into which water will flow based on the design information and drawing information of the nuclear facility as the water level rises.

[0124] Next, a water-stopping method that is expected to be applied as a water-stopping method will be explained using the flowchart in Figure 9. The aforementioned drawings may be referred to as appropriate. The water-stopping method is a method of stopping water by injecting a microparticle dispersion into the inside of a water storage vessel 1 (Figure 1), which is typified by a nuclear reactor containment vessel, for example.

[0125] The flowchart in Figure 9 shows the process from continuing reactor water injection and detecting leak locations to completing water shutdown.

[0126] First, in step S41, the worker continues to inject water and detects the location of the leak.

[0127] In the next step S42, the worker considers measures to stop water leakage. For example, the worker considers measures to prevent water leakage, the area where water will flow out, and the placement of various devices. The worker also checks for an isolation area where the leakage point can be isolated.

[0128] In the next step S43, the worker investigates and identifies the leak location in the water storage section.

[0129] In the next step S44, the worker identifies the location of the leak from the water storage compartment.

[0130] In the next step S45, the worker places a water level gauge and other equipment in the water storage compartment.

[0131] In the next step S46, the worker implements water-stopping measures. For example, the worker injects a microparticle dispersion liquid into the upstream side of the water storage section and arranges various devices for drainage. The worker also arranges various devices in an isolation section that can isolate the leaking point.

[0132] In the next step S47, the worker repeatedly injects the microparticle dispersion into the water storage compartment and drains the water.

[0133] In the next step S48, the worker determines whether or not there is a rise in the water level in the water storage section. If there is a rise in the water level, it is determined that the water stoppage has been effective. Here, if there is a rise in the water level in the water storage section (YES in step S48), the process proceeds to step S49. On the other hand, if there is no rise in the water level in the water storage section (NO in step S48), the process returns to step S47.

[0134] In step S49, which is reached if step S48 is YES, the operator determines whether the amount of leakage and the concentration of radioactive materials are below the allowable values. If they are below the allowable values ​​(YES in step S49), the operator proceeds to step S50. On the other hand, if they are not below the allowable values ​​(NO in step S49), the operator returns to step S47.

[0135] In step S50, which is reached if step S49 is YES, the worker completes the water shutoff.

[0136] For example, as shown in FIG. 1, a pipe 2 serving as a water distribution path (distribution flow path) is connected to a water storage container 1 serving as a water storage compartment. The water storage container 1 has an opening 5 for the pipe 2. This opening 5 is, for example, a nozzle for the pipe 2. The pipe 2 also has a damaged portion 3, which is a water leakage point caused by a severe accident. Water leakage 4 occurs from this damaged portion 3.

[0137] 2, an injection pipe 11 extending from an injection device (not shown) and a drainage pipe 12 extending from a drainage device (not shown) are arranged inside the water storage container 1. Furthermore, a water level indicator (not shown) is also arranged.

[0138] The injection device injects the microparticle dispersion into the water storage container 1 through the injection pipe 11. The water level in the water storage container 1 is prevented from becoming significantly higher than the opening 5 of the pipe 2. When the microparticles contained in the microparticle dispersion settle in the water storage container 1, a supernatant liquid is produced. This supernatant liquid is water separated from the microparticle dispersion.

[0139] A drainage device (not shown) drains this supernatant liquid through a drain pipe 12. In this way, a particulate sediment layer 8 in which particulates are deposited is formed inside the water storage container 1.

[0140] As shown in Figure 3, when a fine particle sediment layer 8 accumulates inside the water storage container 1, the fine particle sediment layer 8 blocks the opening 5 of the pipe 2. As shown in Figure 4, when the opening 5 of the pipe 2 is completely blocked, the water leakage 4 from the broken point 3 can be reduced.

[0141] By injecting the particle dispersion liquid as well as the auxiliary deposit into the water storage container 1, the particle deposit layer 8 can be formed quickly.

[0142] The auxiliary deposits include at least one of jigs and tools, interference materials, heavy muddy water, concrete, grout, mortar, resin, filler, buffer material, zeolite adsorbent, titanate adsorbent, titanium silicate material, neutron absorbing material, cuttings, chips, slag, dross, spatter, abrasives, sand, and mobile robots.

[0143] In addition, in order for workers to determine whether the amount of leakage and the concentration of radioactive materials contained in the leaked water are below the allowable values, equipment for measuring the amount of leakage and equipment for measuring the concentration of radioactive materials are installed in the water storage container 1 and in its vicinity.

[0144] Next, a water stopping method according to a second embodiment will be described with reference to Figures 10 to 12. The aforementioned drawings may be referred to as appropriate. This water stopping method involves, for example, injecting a microparticle dispersion into an isolated space around a leak location and into a water storage vessel 1 serving as a reactor containment vessel.

[0145] As shown in Figure 10, a leak 4 occurs from a pipe 2 serving as a distribution path (distribution flow path) to which a water storage container 1 serving as a water storage compartment is connected. This pipe 2 passes through another isolation container 10 serving as an isolation compartment. A broken portion 3 (leakage portion) exists in part of this pipe 2, and the leak 4 occurs at this broken portion 3. The isolation container 10 has a specified drain outlet 9, and the leaked water 4 from the pipe 2 is drained from the isolation container 10 through this drain outlet 9.

[0146] As shown in FIG. 11 , first, the drain outlet 9 of the isolation container 10 is blocked with a predetermined plug member 20. Next, an injection pipe 11 and a drain pipe 12 are placed in the isolation container 10. Then, a microparticle dispersion is injected into the isolation container 10 from the injection pipe 11. In the isolation container 10, the microparticles in the microparticle dispersion settle, forming a microparticle sediment layer 8. Furthermore, a supernatant liquid is produced from the microparticle dispersion. This supernatant liquid is drained through the drain pipe 12. When the broken portion 3 of the pipe 2 is buried with the microparticle sediment layer 8, the pressure loss in the flow path (flow passage) inside the pipe 2 increases, making it difficult for water to flow.

[0147] As shown in FIG. 12, an injection pipe 11 and a drain pipe 12 are arranged in the water storage container 1. Then, a microparticle dispersion is injected into the water storage container 1 from the injection pipe 11. In the water storage container 1, the microparticles in the microparticle dispersion settle, forming a microparticle sediment layer 8. Furthermore, a supernatant liquid is produced from the microparticle dispersion. This supernatant liquid is drained through the drain pipe 12. By repeatedly injecting and draining the microparticle dispersion, the microparticle sediment layer 8 is quickly deposited, which can block the opening 5 of the piping 2. This can reduce water leakage 4 from the damaged location 3. In this way, a watertight structure is constructed, and the inside of the water storage container 1, i.e., the inside of the reactor containment vessel, can be filled with water and submerged.

[0148] In addition to injecting the microparticle dispersion, an auxiliary deposit may be poured into the water storage container 1 to allow the microparticle deposition layer 8 to be formed quickly.

[0149] Next, a water stopping method according to a third embodiment will be described with reference to Figures 13 to 16. The aforementioned drawings may be referred to as appropriate. This water stopping method involves, for example, crushing the pipe 2 with a pinch device 21 to narrow the flow path (flow passage).

[0150] The specific object of the third embodiment includes a pinch device 21 that crushes at least a part of the pipe 2 that constitutes the distribution path (distribution flow path) so that the distribution path becomes narrow.

[0151] As shown in FIG. 13, a pinch device 21 is placed near the pipe 2 where a leak 4 is occurring. As shown in FIG. 14, the pinch device 21 clamps the pipe 2 and crushes it. In this way, the flow path of the pipe 2 is narrowed, and the pressure loss can be increased. Thereafter, the microparticle dispersion is injected into the water storage container 1 through the injection pipe 11. The supernatant liquid is drained through the drain pipe 12.

[0152] As shown in Figure 15, it becomes difficult for the microparticle dispersion to pass through the crushed portion of the pipe 2, and a microparticle sediment layer 8 quickly accumulates inside the water storage container 1. As shown in Figure 16, the microparticle sediment layer 8 blocks the opening 5 of the pipe 2, and can reduce water leakage 4 from the damaged portion 3. In this way, a watertight structure is constructed, and the inside of the water storage container 1, that is, the inside of the reactor containment vessel, can be filled with water and submerged.

[0153] Next, a water stopping method according to a fourth embodiment will be described with reference to Figures 17 and 18. The aforementioned drawings may be referred to as appropriate. This water stopping method involves, for example, attaching a strainer device 22 to a damaged portion 3 of a pipe 2 to narrow the flow path of leaking water 4.

[0154] The specific object of the fourth embodiment includes a strainer device 22 that narrows the flow path at the leakage point.

[0155] As shown in FIG. 17, a strainer device 22 is fixed to the pipe 2 in which the leaking water 4 is occurring. This strainer device 22 is fixed so as to sandwich the pipe 2. The strainer device 22 is a device that covers the periphery of the pipe 2. The work of fixing the strainer device 22 is performed by remote control. The strainer device 22 also has a mesh. This mesh narrows the flow path of the leaking water 4, increasing the pressure loss in the flow path (flow path) inside the pipe 2.

[0156] As shown in FIG. 18, a microparticle dispersion is injected into the water storage container 1 through an injection pipe 11. The supernatant liquid is drained through a drain pipe 12. A strainer device 22 is provided in the pipe 2, making it difficult for the microparticle dispersion to pass through a broken portion 3 of the pipe 2, and a microparticle sediment layer 8 quickly builds up inside the water storage container 1. The microparticle sediment layer 8 blocks the opening 5 of the pipe 2, reducing water leakage 4 from the broken portion 3. In this way, a watertight structure is constructed, and the inside of the water storage container 1, i.e., the inside of the reactor containment vessel, can be filled with water and submerged.

[0157] Next, a watertight method according to a fifth embodiment will be described with reference to Figures 19 and 20. The aforementioned drawings may be referred to as appropriate. This watertight method involves, for example, cutting a portion of a pipe 2 where a broken portion 3 (Figure 1) exists, and attaching end plugs 23 to both ends of the cut pipe 2 to stop the water from leaking.

[0158] The specific object of the fifth embodiment includes an obstruction that obstructs at least a part of the water flow path (flow passage) that leads to the water storage compartment that can store water. This obstruction is an end plug 23.

[0159] As shown in Figure 19, water inside the water storage container 1 is drained through the drain pipe 12. Drainage continues until the water level inside the water storage container 1 falls below the position (height) of the opening 5 of the pipe 2. When the water level inside the water storage container 1 falls below the position (height) of the opening 5, the water leak 4 that has occurred at the broken point 3 (leak point) of the pipe 2 is stopped.

[0160] Next, a predetermined cutting device (not shown) cuts off the portion of the pipe 2 where the damaged portion 3 (FIG. 1) is located. The cutting operation of the cutting device is performed remotely. The cut portion is then removed.

[0161] As shown in FIG. 20 , end plugs 23 are fixed to both ends of the cut-out portion of the pipe 2 by predetermined attachment devices 24. The end plugs 23 are, for example, crimp plugs fixed to both ends of the pipe 2. In this case, the attachment devices 24 are crimping devices (not shown). The end plugs 23 may also be welded plugs welded to both ends of the pipe 2. In this case, the attachment devices 24 are welding devices (not shown). The end plugs 23 may also be shape-memory alloy plugs that change shape when heated and are fixed to both ends of the pipe 2. In this case, the attachment devices 24 are heating devices (not shown). Thereafter, a microparticle dispersion is injected into the water storage vessel 1 from the injection pipe 11, raising the water level inside the water storage vessel 1. In this way, a water-stopping structure is constructed, and the inside of the water storage vessel 1, i.e., the inside of the reactor containment vessel, can be filled with water and flooded.

[0162] End plugs 23 do not have to completely close both ends of pipe 2, and some water leakage is acceptable. Furthermore, a microparticle dispersion may be injected into water storage container 1 to form microparticle sediment layer 8 (FIG. 4). Even if some water leakage occurs at the end plugs 23, microparticle sediment layer 8 closes pipe 2, thereby reducing water leakage.

[0163] Next, a water stopping method according to a sixth embodiment will be described with reference to Fig. 21. The aforementioned drawings may be referred to as appropriate. This water stopping method involves, for example, placing a balloon 25 as an obstacle in the pipe 2 to narrow the flow path (flow passage).

[0164] The specific object of the sixth embodiment includes an obstacle that hinders the flow of water and a microparticle dispersion. The obstacle is a balloon 25. This balloon 25 narrows the flow path. Note that narrowing the flow path includes blocking the flow path.

[0165] As shown in Fig. 21, a predetermined drilling device (not shown) drills a hole upstream of a broken portion 3 of a pipe 2 where a water leak 4 is occurring. The drilling operation of the drilling device is performed by remote control. Then, a water-stopping material injection pipe 13 is placed in the drilled portion of the pipe 2.

[0166] A predetermined balloon 25 is injected into the inside of the pipe 2 through the waterstop material injection pipe 13. The balloon 25 expands to fill the inside of the pipe 2. The balloon 25 is, for example, a water balloon or a heavy muddy water balloon. The balloon 25 is a material that flows and solidifies, and when injected through the waterstop material injection pipe 13, it narrows the flow path inside the pipe 2.

[0167] For example, an empty balloon 25 is attached to the end of the waterstop material injection pipe 13. Then, the balloon 25 is injected through a perforation formed in the pipe 2. Furthermore, water or heavy muddy water is injected into the balloon 25 through the waterstop material injection pipe 13. In this way, the balloon 25 expands until it comes into close contact with the inner surface of the pipe 2. The balloon 25 narrows the flow path (flow passage) inside the pipe 2, increasing pressure loss.

[0168] Thereafter, the microparticle dispersion is injected into the water storage container 1 through the injection pipe 11. The supernatant liquid is drained through the drain pipe 12. The provision of the balloon 25 in the pipe 2 makes it difficult for the microparticle dispersion to pass through the damaged portion 3 of the pipe 2, and a microparticle sediment layer 8 quickly deposits inside the water storage container 1. The microparticle sediment layer 8 blocks the opening 5 of the pipe 2, and can reduce water leakage 4 from the damaged portion 3. In this way, a watertight structure is constructed, and the inside of the water storage container 1, i.e., the inside of the reactor containment vessel, can be filled with water and submerged.

[0169] Furthermore, instead of the balloon 25, a material such as concrete, grout, mortar, filler, buffer material, or resin may be injected into the pipe 2 through the waterstop material injection pipe 13 as an obstacle and allowed to harden. In this way, the same effect as that of the balloon 25 can be obtained.

[0170] Next, a water stopping method according to a seventh embodiment will be described with reference to Figures 22 and 23. The aforementioned drawings may be referred to as appropriate. This water stopping method involves, for example, injecting a microparticle dispersion containing an aggregation promoter 26 from the upstream side of the water storage container 1 to narrow the flow path (flow passage) of the pipe 2.

[0171] The specific object of the seventh embodiment includes an obstacle that remains in the water flow path leading to the water storage compartment where water can be stored and obstructs the flow of water. The obstacle is a coagulation promoter 26. This coagulation promoter 26 narrows the flow path. Note that narrowing the flow path includes blocking the flow path.

[0172] As shown in Fig. 22, an aggregation-promoting device 27 is placed near the pipe 2. This placement is performed by remote control. Then, a microparticle dispersion containing an aggregation-promoting material 26 is injected into the water storage container 1 through an injection pipe 11.

[0173] The agglomeration promoter 26 is, for example, magnetic powder or iron powder, which is a metal powder that acts on magnetic force. The agglomeration promoter 27 is, for example, a magnetizing device that applies magnetic force. The magnetic powder is agglomerated by applying a magnetic field from the outside of the pipe 2 using the magnetizing device. Then, an agglomerated portion 26A is generated where the agglomeration promoter 26 has agglomerated. Here, whether the pipe 2 is made of a non-magnetic or magnetic material, the magnetic powder agglomerates due to magnetic attraction, generating the agglomerated portion 26A, and narrowing the flow path (flow passage) inside the pipe 2.

[0174] Furthermore, aggregation promoter 26 may be a low-melting-point material such as gallium or low-melting-point glass. Aggregation promoter 27 is, for example, a heating device. By disposing a heating device outside pipe 2 and heating pipe 2, the low-melting-point material is melted. Furthermore, on the downstream side of pipe 2, the low-melting-point material is cooled and solidified. As a result, the low-melting-point material and the fine particles aggregate, narrowing the flow path inside pipe 2.

[0175] Furthermore, the aggregation accelerator 26 may be a freezing accelerator. The aggregation accelerator 27 is, for example, a cooling device. By disposing a cooling device outside the pipe 2 and cooling the pipe 2, the freezing accelerator freezes the microparticle dispersion. This freezing narrows the flow path inside the pipe 2. When freezing, a microparticle dispersion that does not contain a freezing accelerator may be used.

[0176] 23, the coagulation accelerator 26 coagulates inside the pipe 2, forming a coagulated portion 26A, which makes it difficult for the microparticle dispersion to pass through. As a result, a microparticle sediment layer 8 is deposited early, blocking the opening 5 of the pipe 2 and reducing water leakage 4 from the damaged portion 3. In this way, a watertight structure is constructed, and the inside of the water storage vessel 1, i.e., the inside of the reactor containment vessel, can be filled with water and submerged.

[0177] Next, a water stopping method according to an eighth embodiment will be described with reference to Fig. 24 to Fig. 26. The aforementioned drawings may be referred to as appropriate. This water stopping method involves, for example, injecting water glass 28, which acts as an obstacle, into the pipe 2 to narrow the flow path (flow passage).

[0178] The specific object of the eighth embodiment includes an obstacle that remains in the water flow path leading to the water storage compartment where water can be stored and obstructs the flow of water. The obstacle is water glass 28. This water glass 28 narrows the flow path. Note that narrowing the flow path includes blocking the flow path.

[0179] As shown in Figure 24, a water leak 4 is occurring from a pipe 2 serving as a distribution path connected to a water storage container 1 serving as a water storage compartment. This pipe 2 passes through another isolation container 10 serving as an isolation compartment. A damaged portion 3 (leakage portion) is present in a portion of this pipe 2, and the water leak 4 is occurring at this damaged portion 3.

[0180] A predetermined drilling device (not shown) drills a hole upstream of the broken point 3 in the pipe 2 where the leak 4 is occurring. The drilling operation by the drilling device is performed remotely. A water-stopping material injection pipe 14 is then placed in the drilled portion of the pipe 2. Also, a gas injection pipe 15 for injecting carbon dioxide gas 29 is placed in the isolation container 10. When the water glass 28 acting as an obstacle comes into contact with the carbon dioxide gas 29, its solidification is accelerated.

[0181] The water inside the water storage container 1 is drained through the drain pipe 12. Drainage continues until the water level inside the water storage container 1 falls below the position (height) of the opening 5 of the pipe 2. When the water level inside the water storage container 1 falls below the position (height) of the opening 5, the leakage 4 occurring at the broken point 3 (leak point) of the pipe 2 is stopped.

[0182] As shown in Figure 25, water glass 28 is injected into the inside of the pipe 2 through the water-stopping material injection pipe 14. The inside of the pipe 2 is filled with the water glass 28. Furthermore, carbon dioxide gas 29 is injected into the inside of the isolation container 10 through the gas injection pipe 15 and fills it. Furthermore, the carbon dioxide gas 29 also enters the inside of the pipe 2 and fills the inside of the water storage container 1 as well.

[0183] The water glass 28 is a material that flows and solidifies, and when injected from the waterstop material injection pipe 14, it narrows the flow path inside the pipe 2. Furthermore, the carbon dioxide gas 29 promotes the solidification of the water glass 28. In this way, the solidification of the water glass 28 inside the pipe 2 is promoted, the water glass 28 solidifies quickly, and the broken portion 3 can be sealed with the water glass 28.

[0184] 26, water is then injected into the water storage vessel 1 from the injection pipe 11. In this way, a watertight structure is constructed, and the inside of the water storage vessel 1, i.e., the inside of the reactor containment vessel, can be filled with water and submerged.

[0185] Next, a water stopping method according to a ninth embodiment will be described with reference to Figures 27 and 28. The aforementioned drawings may be referred to as appropriate. This water stopping method involves, for example, inserting a plurality of weir materials 30 into a pipe 2 to act as obstacles, thereby narrowing the flow path (flow passage).

[0186] The specific object of the ninth embodiment includes an obstacle that remains in the water flow path leading to the water storage compartment where water can be stored and hinders the flow of water. The obstacle is a weir material 30. This weir material 30 narrows the flow path. Note that narrowing the flow path includes blocking the flow path.

[0187] As shown in FIG. 27, an injection pipe 11 and a drainage pipe 12 are arranged inside the water storage container 1, and an injection pipe 16 for injecting a weir material 30 is also provided.

[0188] A microparticle dispersion is injected from injection pipe 11 while the supernatant liquid is drained from drain pipe 12, thereby maintaining a predetermined water level inside water storage container 1. Then, weir material 30 is introduced into water storage container 1 from input pipe 16. Here, since water leakage 4 is occurring from damaged portion 3 of pipe 2, introduced weir material 30 enters pipe 2 along with the flow of water.

[0189] The weir material 30 includes, for example, materials such as neutrally buoyant closed-cell foam beads, highly water-absorbent resin, water-expanding rubber, a bag member, and neutrally buoyant magnetic beads.

[0190] First, we will explain the case where the weir material 30 is made of neutrally buoyant closed-cell foam beads, a superabsorbent resin, or water-expanding rubber. This weir material 30 flows into the pipe 2 together with the microparticle dispersion and reaches the vicinity of the damaged portion 3 (leak portion). There, the weir material 30 gradually expands as the pressure decreases and the time of contact with water passes.

[0191] In addition, the weir material 30 is exemplified as a bag member or neutrally buoyant magnetic beads. The volume and weight of the contents of this weir material 30 are adjusted so that it is neutrally buoyant in water. Here, the weir material 30 flows toward the pipe 2 along with the flow of the microparticle dispersion liquid and remains inside the pipe 2.

[0192] As shown in Figure 28, when the weir material 30 is made of neutrally buoyant magnetic beads, the neutrally buoyant magnetic beads are magnetically attracted to each other. As a result, the weir material 30 can remain inside the pipe 2 and block the pipe 2. Furthermore, it can promote the deposition of the fine particle sediment layer 8. In this way, a watertight structure is constructed, and the inside of the water storage vessel 1, i.e., the inside of the reactor containment vessel, can be filled with water and submerged.

[0193] The weir material 30 may be mixed in advance with the microparticle dispersion and then poured into the water storage container 1 through the injection pipe 11.

[0194] Next, a water stopping method according to a tenth embodiment will be described with reference to Fig. 29 and Fig. 30. The aforementioned drawings may be referred to as appropriate. This water stopping method involves, for example, inserting multiple drones 31 into a pipe 2 as obstacles to narrow the flow path (flow passage).

[0195] The specific object of the tenth embodiment includes an obstacle that remains in a water flow path leading to a water storage compartment capable of storing water and obstructs the flow of water. The obstacle is a drone 31. This drone 31 narrows the flow path. Note that narrowing the flow path includes blocking the flow path. For example, one drone 31 may be an obstruction that blocks the flow path.

[0196] The tenth embodiment of the water stopping method involves moving an obstacle with a mobile robot and placing the obstacle at a predetermined position related to a circulation path, including a case where the mobile robot itself is the obstacle.

[0197] As shown in Figure 29, an inlet pipe 11 and a drain pipe 12 are placed inside the water storage container 1, and multiple drones 31 are also placed inside. The drones 31 are small underwater robots that move underwater by remote control. Alternatively, the drones 31 may be autonomous.

[0198] A microparticle dispersion is injected from injection pipe 11 while the supernatant liquid is drained from drain pipe 12, thereby maintaining a predetermined water level inside water storage container 1. Then, drone 31 is dropped into water storage container 1. Here, the dropped drone 31 enters pipe 2. Then, drone 31 stops at a set target position.

[0199] When the set target position is an opening 5 of the pipe 2, the multiple drones 31 form a weir at the opening 5. This narrows the flow path of the pipe 2. Alternatively, the drones 31 may transport a weir material 30 (FIG. 27) that is an obstacle, and this weir material 30 may narrow the flow path.

[0200] 30, the drone 31 can remain inside the pipe 2 and block the pipe 2. Furthermore, it can promote the deposition of the fine particle sediment layer 8. In this way, a watertight structure is constructed, and the inside of the water storage vessel 1, i.e., the inside of the reactor containment vessel, can be filled with water and submerged.

[0201] The drone 31 may be an aerial robot that flies in the air. For example, the water level may be lowered in the drain pipe 12, and then the drone 31 may be deployed in the air. The drone 31 may then approach the opening 5 of the pipe 2 from the air and close the opening 5. The drone 31 may also approach the opening 5 while floating on the water surface. Furthermore, the drone 31 may approach the opening 5 from underwater near the water surface. The drone 31 may also be a remote-controlled boat that moves on the water.

[0202] Next, a water stopping method according to an eleventh embodiment will be described with reference to Figures 31 and 32. The aforementioned drawings may be referred to as appropriate. This water stopping method narrows the flow path (flow passage) by, for example, introducing a plurality of blocking materials 32 from the outside and inside of a pipe 2.

[0203] The specific object of the eleventh embodiment includes an obstacle that remains in the water flow path leading to the water storage compartment where water can be stored and obstructs the flow of water. The obstacle is a blocking material 32. This blocking material 32 narrows the flow path. Note that narrowing the flow path includes blocking the flow path.

[0204] As shown in FIG. 31, an injection pipe 11 and a drain pipe 12 are arranged inside the water storage container 1, and an injection pipe 17 for injecting a blocking material 32 is also provided.

[0205] A microparticle dispersion is injected through injection pipe 11, while the supernatant liquid is drained through drain pipe 12, thereby maintaining a predetermined water level inside water storage container 1. Then, plugging material 32 is injected into water storage container 1 through injection pipe 17. Further, plugging material 32 is injected near the outside of pipe 2. The plugging material 32 is sprayed in an aerial environment. Then, the plugging material 32 adheres to the inside and outer periphery of pipe 2.

[0206] The blocking material 32 includes, for example, powder such as calcium borate that easily adheres to wet surfaces, thermal spraying, sprayed mortar, and a material such as a superabsorbent resin that absorbs water and expands.

[0207] As shown in Figure 32, the plugging material 32 adheres to and accumulates on the outer peripheral surface of the damaged portion 3 (leakage portion) of the pipe 2. The plugging material 32 also blocks the opening 5 of the pipe 2. The plugging material 32 adheres to and accumulates inside the pipe 2, making it difficult for the microparticle dispersion to pass through the pipe 2. This promotes the accumulation of the microparticle deposition layer 8. In this way, a watertight structure is constructed, and the inside of the water storage vessel 1, i.e., the inside of the reactor containment vessel, can be filled with water and submerged.

[0208] Next, a water stopping method according to a twelfth embodiment will be described with reference to Fig. 33. The above-mentioned drawings may be referred to as appropriate. In this water stopping method, for example, the opening 5 of the pipe 2 is plugged with a plugging plug 33.

[0209] The specific object of the twelfth embodiment includes a blocking object that blocks at least a part of a water flow path (flow passage) leading to a water storage compartment that can store water.

[0210] 33, water can be stored in the water storage container 1 by plugging the opening 5 of the pipe 2 with a plugging plug 33. In this way, a watertight structure is constructed, and the inside of the water storage container 1, i.e., the inside of the reactor containment vessel, can be filled with water and submerged.

[0211] In designing the plugging plug 33, the three-dimensional shape of the inner surface of the opening 5 of the pipe 2 may be measured in advance so that the plugging plug 33 fits into the opening 5.

[0212] Even if the opening 5 is plugged with the plug 33, there may be some water flow through the plug 33. In this case, a microparticle dispersion may be poured into the water storage container 1 to form the microparticle sediment layer 8 (FIG. 4). Alternatively, an auxiliary deposit may be poured into the water storage container 1 to accelerate the formation of the microparticle sediment layer 8.

[0213] Next, a water stopping method according to a thirteenth embodiment will be described with reference to Fig. 34. The above-mentioned drawings may be referred to as appropriate. This water stopping method stops water flow after, for example, injecting clean water into a pipe 2.

[0214] As shown in Figure 34, inside the water storage container 1, a clean water injection pipe 18 is placed near the opening 5 of the pipe 2. Clean water is injected from an injection nozzle 19 at the tip of this clean water injection pipe 18 toward the opening 5 of the pipe 2. In other words, clean water is injected from the opening 5 on the upstream side of the water distribution path (distribution flow path) leading to the water storage compartment where water can be stored, and water contaminated with radioactive materials leaking from the leak point is replaced with clean water. This also makes it possible to dilute the radioactive materials. It also makes it possible to clean the inside of the pipe 2. Thereafter, the leak point is sealed off as in the above-mentioned embodiment.

[0215] As described above, according to the above-described embodiment, the fuel debris to be removed and the structures to be dismantled are submerged in water.

[0216] In addition, it is possible to stop leaks in a flooded environment, collect, store, and purify the leaked water, and circulate it between the water storage tank and the reactor building. This allows the water level inside the reactor containment vessel (reactor building) and the water storage tank to be maintained, and fuel debris and structures to be dismantled to be removed while they are submerged.

[0217] The present invention has been described above based on the first to thirteenth embodiments, but the configuration applied in any of the embodiments may be applied to other embodiments, and the configurations applied in each embodiment may be combined.

[0218] In the above-described embodiment, the manner in which a microparticle deposition layer 8 is formed to seal off the leaking area includes not only the manner in which a microparticle deposition layer 8 is formed inside the room in which the leaking area is located to seal off the water, but also the manner in which a microparticle deposition layer 8 is formed outside the room in which the leaking area is located to seal off the water.

[0219] In the above-described embodiment, "flooding" includes submerging the equipment from which fuel debris is to be removed and structures to be removed that obstruct access when removing the fuel debris. "Flooding" also includes filling the interior of the equipment to be removed with water when removing fuel debris. "Flooding" also includes submerging highly radioactive parts of the equipment to be removed to a depth at which the radiation level is sufficiently attenuated when removing fuel debris.

[0220] In the above-described embodiments, the singular does not necessarily mean to limit the number to one, and the singular may mean a plural number.

[0221] Although the above-described embodiment exemplifies a form applied to the decommissioning of a boiling water reactor (BWR), other forms may also be used. For example, the above-described embodiment may be applied to the decommissioning of an advanced boiling water reactor (ABWR), a pressurized water reactor (PWR), or a graphite-moderated boiling water pressure tube reactor (RBMK).

[0222] According to the embodiment described above, by constructing a watertight structure that uses at least one specific material to stop water leaking from the leaking area, it is possible to flood at least a portion of a nuclear facility that has suffered a severe accident, shield radiation with water, and enable work to be done in an underwater environment.

[0223] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and modifications thereof are intended to be included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0224] 1...water storage container, 2...piping, 3...damaged area, 4...leak, 5...opening, 6...gas phase area, 7...water area, 8...fine particle deposition layer, 9...drain outlet, 10...isolation container, 11...injection pipe, 12...drain pipe, 13, 14...waterstop material injection pipe, 15...gas injection pipe, 16, 17...inlet pipe, 18...clean water injection pipe, 19...spray nozzle, 20...plug member, 21...pinch device, 22...strainer device, 23...end plug, 24...mounting device, 25...balloon, 26...coagulation promoter, 26A...coagulation portion, 27...coagulation promoter, 28...water glass, 29...carbon dioxide, 30...dam material, 31...drone, 32...blocking material, 33...plug

Claims

1. When a water leakage point exists in a water flow path leading to a water storage compartment that is capable of storing water, the water leakage point is stopped by constructing a water stop structure that uses at least one specific material between the water storage compartment and the leakage point, in a compartment related to a nuclear facility where fuel debris has been generated due to a severe accident, introducing water into the water storage compartment to flood at least a portion of the nuclear facility; Methods for flooding nuclear facilities.

2. The specific substance includes a microparticle dispersion liquid containing microparticles having a specific gravity greater than that of water. The method for flooding a nuclear facility according to claim 1.

3. The microparticles include at least barite as a weighting material and at least bentonite as a thickening agent. The method for flooding a nuclear facility according to claim 2.

4. the microparticles include two or more types of barite, bentonite, a polymer, a nuclide adsorbent, and boric acid, and are a combination of the microparticles having different particle sizes; The method for flooding a nuclear facility according to claim 2.

5. forming a particulate deposition layer in an internal space of the nuclear facility associated with the leak location by depositing the particulates until the particulates reach a height higher than the leak location; The method for flooding a nuclear facility according to claim 2.

6. The fine particles and auxiliary deposits are alternately introduced into the internal space; the layers of the fine particles and the layers of the auxiliary deposit are alternately deposited to form a multi-layered fine particle deposition layer; The method for flooding a nuclear facility according to claim 5.

7. The auxiliary deposit includes at least one of jigs and tools, interference materials, heavy muddy water, concrete, grout, mortar, resin, filler, buffer material, zeolite adsorbent, titanate adsorbent, titanium silicate material, neutron absorbing material, cuttings, chips, slag, dross, spatter, abrasives, sand, and mobile robots. The method for flooding a nuclear facility according to claim 6.

8. the specific object includes an obstacle that hinders the flow of water and a microparticle dispersion liquid containing at least microparticles having a specific gravity greater than that of water; The obstacle is used to narrow the flow path; The water-stopping structure is constructed using the microparticle dispersion. The method for flooding a nuclear facility according to claim 1.

9. The specific object includes an obstacle that remains in the flow path and hinders the flow of water. The method for flooding a nuclear facility according to claim 1.

10. The obstacle includes at least one of a jig, an interference material, heavy muddy water, concrete, grout, mortar, a resin, a filler, a buffer material, a zeolite adsorbent, a titanate adsorbent, a titanium silicate material, a neutron absorbing material, cuttings, chips, slag, dross, spatter, abrasives, sand, and a mobile robot. The method for flooding a nuclear facility according to claim 8 or 9.

11. moving the obstacle with a mobile robot and placing the obstacle at a predetermined position related to the distribution flow path; The method for flooding a nuclear facility according to claim 8 or 9.

12. The specific object includes an obstruction that obstructs at least a portion of the flow path. The nuclear facility flooding method according to any one of claims 1 to 9.

13. The specified object includes a pinch device that crushes at least a part of a pipe that constitutes the flow path so that the flow path becomes narrow. The nuclear facility flooding method according to any one of claims 1 to 9.

14. The specified object includes a strainer device that narrows the flow path at the leakage point. The nuclear facility flooding method according to any one of claims 1 to 9.

15. Injecting clean water from an opening on the upstream side of the distribution flow path to replace water contaminated with radioactive materials leaking from the leakage point with the clean water. The nuclear facility flooding method according to any one of claims 1 to 9.

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